1. Field of the Invention
The present invention relates to a magnetic circuit switching device with single-sided attraction, particularly to one that has two magnetic circuits and a single-sided attraction structure for a displaceable iron core to have a wider stretching range in operation.
2. Description of the Related Art
The theory of magnetic field effect has been widely applied to valves, solenoids, and relays. A conventional solenoid valve attracts an iron core thereof by a magnetic force produced by an energized coil to open a valve port thereof. However, such solenoid valve has to keep energizing the coil to attract the iron core aside and keep a fixed position of the iron core, so as to keep the valve port opened. Therefore, it needs a great amount of power supply, and the solenoid valve would be overheated and burned by a short circuit after continuous operation.
The present inventor has therefore disclosed a magnetic power apparatus in U.S. Pat. No. 6,246,131 and a magnetic device with double fixing positions for changing the magnetic circuit in U.S. Pat. No. 6,057,750. The structure of a magnetic power apparatus 100 is illustrated in FIGS. 1A and 1B, including an outer shell 101, a coil 102, an iron core 103, a permanent magnet 104, a left attraction surface 105, and a right attraction surface 106. When the coil 102 is energized, the iron core 103 displaces leftwards or rightwards due to the magnetic force from the coil 102 or the permanent magnetic 104. Such structure has both sides to fixedly keep the position of the iron core 103 in operation by the permanent magnet 104, so it does not need continuous electricity supply, thus being energy-saving and preventing the invention from overheating and burning by a short circuit. The safety and durability are therefore ensured in the improved structure. However, the stretching range D of the iron core 103 is restricted due to the double sided fixing position; that is, the right attraction surface 106 is a closed structure 107. If the stretching range D is design to be 5 mm, the iron core 103 can only displaces exactly 5 mm, shorter or further is impossible. In this case, when an applied device (not shown) has deviation or wear and tear, the operation would be affected. Either the design is the permanent magnet 104 in a column shape with the iron core 103 disposed around the permanent magnet 104 as shown in FIGS. 1A and 1B, or the design is the permanent magnet 104 in a ring shape with the iron core 103 disposed in-between a plurality of permanent magnets 104 as shown in FIGS. 5 and 6 in the U.S. Pat. No. 6,246,131, the defect would affect the operation.
Consequently, the inventor has devoted to improving the restriction defect of the stretching range of the iron core 103.